This nonprovisional application claims priority under 35 U.S.C. xc2xa7119(a) on Patent Application No. 88553/2001 filed in Korea on Dec. 29, 2001, which is herein incorporated by reference.
1. Field of the Invention
The invention relates to an ink printing device for pattern formation, and more particularly, to an ink printing clichxc3xa9 capable of forming a fine pattern and lengthening the life span of a printing device by forming a clichxc3xa9 with an organic material or an organic/metal.
2. Description of the Related Art
Display devices, especially a flat panel display such as a liquid crystal display (LCD) device, include an active device such as a thin film transistor (TFT) in each pixel to drive the display device. This display device driving method is called an active matrix driving method. In an active matrix method, the active driving device is disposed in each pixel. The pixels are arranged in a matrix. FIG. 1 illustrates an active matrix liquid crystal display device, in which the liquid crystal display device is a TFT LCD using a thin film transistor as the active device.
As shown in FIG. 1, the TFT LCD has Nxc3x97M pixels vertically and horizontally arranged. Each pixel has a gate line 4 to which a scan signal is applied from an external driving circuit, a data line 6 to which an image signal is applied, and a TFT formed at the intersection of the gate line 4 and the data line 6.
The TFT includes a gate electrode 3 connected to the gate line 4. A semiconductor layer 8 is formed on the gate electrode 3, and the semiconductor layer 8 activates when a scan signal is applied to the gate electrode 3. A source/drain electrode 5 is formed on the semiconductor layer 8.
A pixel electrode 10 is formed at a display region of the pixel 1, and the pixel electrode 10 connects to the source/drain electrode 5. An image signal is applied through the source/drain electrode 5 as the semiconductor layer 8 is activated, to thereby activate a liquid crystal (not shown).
The source/drain electrode 5 of the TFT is electrically connected to the pixel electrode 10 formed in the pixel 1, so that as a signal is applied to the pixel electrode 10 through the source/drain electrode 5, the source/drain electrode 5 drives the liquid crystal and displays an image.
In the active matrix type display device such as the liquid crystal display device, each pixel has a size of scores of xcexcm. Thus, the active device such as the TFT disposed in the pixel should have a fine size, i.e., a few xcexcm.
In addition, high picture quality display devices such as the high definition (HD) TV have been in increasing demand. These devices require a greater concentration of pixels occupying a screen of the same area. As a result, the active device pattern (including gate line and data line patterns) disposed on the pixel also becomes more dense and requires a finer structure.
In the conventional art, fabrication of an active device, such as a TFT, utilizes a pattern or a line of the active device formed by a photolithography method using an exposure device.
However, this photolithography method uses a high-priced exposing device. The steps of photolithography can include vapor prime, spin coat, soft bake, alignment and exposure through a mask, post-exposure bake, development, hard bake and inspection. The result is increased fabrication cost and a complicated fabrication process.
Additionally, the exposure region of the exposing device is limited in the photolithographic production of a display device. In order to fabricate a large-scale display device, the screen is divided to accommodate the photolithographic process. This degrades productivity because it is difficult to accurately match the positions when processing the divided regions, and the photolithographic process has to be repeated several times.
In order to solve this problem, pattern forming by gravure offset printing has been recently proposed.
Gravure offset printing is a printing method in which ink is put on a concave plate. Redundant ink is removed by scraping or doctoring, and then printing is performed. This printing method has been adopted in various applications such as printing wrappings of cellophane, vinyl or polyethylene.
Recently, efforts have been made to adapt gravure printing to produce an active device used for the display device or to produce a circuit pattern.
Gravure offset printing transfers ink to a substrate by using a transfer roll, and a pattern can be formed by a single printing step. Even a large-scale display device can be produced by using a transfer roll corresponding to the area of the desired display device.
Gravure offset printing can be used to pattern various configurations and sub-assemblies of the display device. These can include, for example, a metal pattern for a capacitor, a pixel electrode, the gate line and the data line connected to the TFT, and the TFT, which are all structures necessary for a liquid crystal display device.
FIGS. 2A through 2C illustrate pattern forming by a conventional gravure offset printing method.
As shown in FIG. 2A, the conventional gravure offset printing method forms a groove 22 at a specific position of a clichxc3xa9 20 or a concave plate. The groove 22 corresponds to a pattern that is desired to form on a substrate. The groove 22 is filled with ink 24.
The ink 24 in the groove 22 results in pattern forming ink 24 being coated at an upper portion of the clichxc3xa9 20, and then a doctor blade 28 proceeds while in contact with the clichxc3xa9 20. A doctor blade 28 proceeds to impress the ink 24 filled into the groove 22. The doctor blade simultaneously removes the excess ink 24 remaining on the surface of the clichxc3xa9 20. Alternatively, a Meyer rod can be used instead of a doctor blade.
As shown in FIG. 2B, the ink 24 filling in the groove 22 of the clichxc3xa9 20 contacts and transfers to the surface of the transfer role 30.
The transfer roll 30 is formed with a circumference having the same length as that of the panel of a display device to be fabricated. That is, the transfer roll 30 has the circumferential length equal to the length of the desired panel. Accordingly, the ink 24 filled in the groove 22 of the clichxc3xa9 20 can be wholly transferred on the surface of the circumference of the transfer roll 30 by a single rotation.
Thereafter, as shown in FIG. 2C, the transfer roll 30 contacts the surface of a process-object layer 41 formed on the substrate 40, and the transfer roll 30 is rotated. Then, the ink 24 transferred on the transfer roll 30 is re-transferred on the process-object layer 41. By applying heat to the re-transferred ink 24 and drying it, an ink pattern 42 is formed. At this time, the desired ink pattern 42 can be formed on the entire substrate 40 of the display device by a single rotation of the transfer roll 30.
In the gravure offset printing method discussed above, since the ink pattern 42 is mechanically formed by using the clichxc3xa9 20, and the transfer roll 30 and the process-object layer 41 is etched by the ink pattern 42 to form a desired pattern, the pattern forming process is simplified compared to the conventional photolithographic exposure process.
However, the conventional art gravure offset method has shortcomings. Generally, since the clichxc3xa9 20 is made of a metal such as ferrite and nickel, it is difficult to form a fine groove.
Usually, the groove 22 of the clichxc3xa9 20 is formed by a mechanical process. In this respect, it is not substantially possible to mechanically process a groove of below a few xcexcm. Thus, it is difficult to form a fine ink pattern, and this process can scarcely be adopted to fabricate a display device.
In addition, the surface of the metal clichxc3xa9 20 becomes damaged due to abrasion by the doctor blade 28, and particles are generated. These particles are a critical factor leading to pattern defects during formation of an ink pattern. Moreover, since the grain is large, a rough edge region of the groove is formed when the groove is processed, which makes it impossible to form a smooth ink pattern.
As has been shown, the conventional art gravure process using a clichxc3xa9 has serious drawbacks that hamper adaptation of this technology to the production of semiconductor devices such as liquid crystal displays.
The invention, in part, provides a clichxc3xa9 of a gravure offset printing device and its fabrication method that are capable of forming a fine ink pattern and a final fine pattern by forming the clichxc3xa9 with an organic material.
The invention, in part, provides a clichxc3xa9 of a gravure offset printing device and its fabrication method that are capable of forming a fine pattern having a lengthened life span by forming a clichxc3xa9 with an organic material/metal.
To achieve these and other advantages and in accordance with the invention, there is provided a gravure offset printing device including a clichxc3xa9 with a groove formed in which ink is filled and a transfer roll for re-transferring the ink transferred from the clichxc3xa9 to a process-object layer, wherein the clichxc3xa9 includes a substrate and an organic layer with a groove formed in a portion of the organic layer.
In the gravure offset printing device of the invention, the substrate is made of glass, plastic or semiconductor wafer, and the organic layer is made of a polymer, polyimide, photosensitive acrylate or methacrylate, or BCB (Benzocyclobutene). The organic layer is grain-free.
In the invention, a metal layer may be formed over the organic layer to lengthen the life span of the clichxc3xa9, and an intermediate layer can be formed to improve the adhesion force between the organic layer and the metal layer.
The invention, in part, pertains to a clichxc3xa9 fabrication method including the steps of preparing a substrate, depositing an organic layer and a photoresist layer over the substrate, developing the photoresist layer to form a photoresist pattern, and etching the organic layer while the organic layer is blocked with the photoresist pattern, to form a groove.
The foregoing and other objects, features, aspects and advantages of the invention will become more apparent from the following detailed description of the invention when taken in conjunction with the accompanying drawings, which provide further explanation of the invention, as claimed.